1. Field of the Invention
The invention relates to the field of joints or couplings for electric power cables and more specifically to the field of submarine electric power cable couplings or terminations.
2. Description of the Prior Art
U.S. Pat. No. 2,142,884 discloses an electric power cable joint having conductors enclosed within an inner lead sheath which is further enclosed within a second lead insulating sheath. The insulating sheaths are wrapped with a layer of armored winding wires, the ends of which are secured to armored clamps.
U.S. Pat. No. 1,647,699 discloses an electric cable joint having a cable splice housing threadably attached to an armor termination housing.
U.S. Pat. No. 2,449,983 discloses an electric power line coupling having an inner conductor surrounded by an insulating layer which is further surrounded by an outer conductor comprising a copper braid. The ends of the copper braid contact an incline surface of a metallic member which in turn contacts a second metallic member. In this way, electrical contact is established between the wire braids 13 through the coupling.
U.S. Pat. No. 4,259,543 discloses a submarine electric power cable termination having a cone for mechanically anchoring the armored winding wires and having an outer serving for insulating both the armored winding wires and an inner insulating sheath from the sea environment.
The manufacturing and installation of multi-conductor high voltage power cable requires the use of factory jointing techniques. Such cables can only be produced in continuous (i.e., jointless) lengths up to the volume and weight limits of the cabling machine bobbins. For multi-conductor cables that must be cabled (twisted together) the length limits are typically in the 1 to 2 kilometer range. Submarine power cables are often longer than 2 kilometers.
Factory joints installed in submarine power cables are typically subjected to high tension and bending stresses during handling, installation and use. Due to these unusual stresses, submarine power cable joints are designed differently than land-based power cable joints. Land-based cables are always installed first and then jointed so that such joints are never subjected to the bending and the high forces that occur in submarine power cable splices. Also, land-based cables seldom have the protective armored winding layers present in submarine cables to provide protection against torsional loads placed on the cable.
During typical submarine cable system operation, both continuous and transient electrical potentials occur between the lead sheath of the cable and the armor, and between the lead sheath and the sea which could result in destruction of the lead sheath. Since the electrical integrity of the underlying PILC or SCOF electrical insulation depends upon the hermetic seal provided by the lead sheath, destruction (puncturing or cracking) of the lead sheath leads to electrical failure of the power cable.